A corrugated tube compensator, for instance of the type usable as an expansion joint between straight lengths of pipe, is formed with a plurality of annular nonhelical corrugations. Such a shape is relatively difficult to make. Forming it by rolling up an appropriately corrugated sheet has been found impossible, so that recourse has been had to making it, corrugation at a time, by making U-section rings and then welding them together.
In my German patent application No. 2,831,202, published Jan. 24, 1980, I describe an apparatus for forming annular corrugations in a short cylindrical tube. This apparatus has a pair of shafts centered on and rotatable about respective shaft axes. One of these shafts is radially displaceable toward and away from the other. A central disk is fixed on one of the shafts and is flanked by a pair of axially displaceable outer disks. A pair of axially displaceable roller disks are provided on the other shaft each lying between a respective one of the outer disks of the one shaft and the central disk. Thus the disks are interleaved.
A main drive is connected mechanically to both of the shafts for synchronously and oppositely rotating same. In addition each of the shafts is associated with a respective spindle threadedly engaging the displaceable roller disks and rotatable to move the roller disks toward or away from one another. Each of these spindles has at its outer end a pinion meshing with a main drive gear carried directly on the respective shaft so that the axial advance of each of the roller disks will be exactly proportional to the rotation rate for the respective shafts.
In use a tubular sleeve is fitted over one of the shafts which is then moved toward the other shaft so as to lightly grip the tube between the roller disks. Then the two shafts are simultaneously rotated and urged radially toward each other. At the same time the disks move axially inwardly so that the entire tube is regularly deformed to have annular nonhelical corrugations.
Such a system is an enormous advance over the prior-art method of piecemeal assembly of a corrugated tube compensator. Nonetheless certain problems remain. In particularly thick tubes, for example, it is occasionally difficult to axially advance the roller disks toward one another and to radially displace the shafts toward one another at a relatively high speed, but it is necessary to move the roller disks at a high peripheral speed. Thus a tradeoff must be made between ideal rolling speed and axial advance speed for the roller disks. Furthermore the axial advance of the disks is directly proportional to the rotation rate, so that as soon as the device is started up the disks start to move axially together.